Dhofar Power Company SAOG

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All members with an inclination of less than 40 degrees to the horizontal, shall be checked for the effects
of point loading of 1.5 kN at its most onerous position. No other loading shall be considered under this
condition.
It is the Contractor's responsibility to consider all constructional loading due to his proposed method of
support erection and conductor stringing. Where necessary, any additional loading due to these methods
shall be considered in the design of the support and especially the specified maintenance, lifting or
attachment points. Under these conditions a minimum partial safety factor of 1.5 shall be considered.
7.2.7 Downlead Tensions
The maximlllll downlead tension shall be 1200 kg. However, for the purpose of support design they shall
be assumed to be zero except where the vertical load component increases the stresses in support
members. These tensions shall be assumed to apply at both ends on low duty tension insulator sets.
7.2.8 Ultimate Applied Loading
Factor of safety to be used for tower design is specified in Appendix 7A3.
7.2.9 Allowable Ultimate Stresses
The allowable ultimate stresses used in the determination of the nominal strength of support members
shall be based on the following criteria:
(a) For lattice steel tower stresses shall be based on the recommendations contained in BS DD 133 or
ANSI/ASCE Std 10-90. For Std 10-90 the appropriate reference stress levels shall be based on
the values specified in BS 5950, and as summarised below:
Grade Reference Stress Level (N/mm
2
)
S235JRG2
S275JR
S355JO
235
225
275
265
355
345
< 16 mm (Nominal Thickness)
> 16 <40 mm
< 16mm
> 16 <40 mm
< 16mm
>16 <40 mm
(b) For lattice steel tower where the appropriate design stresses are not contained in the specified
code of practice / manual, reference shall be made to BS 5950;
7.2.10 Design Criteria
The maximum allowable slenderness ratios for members of lattice steel towers shall be:
•
•
•
•
•
For leg members, cross arm chords
For other load bearing compression members
For secondary bracings
For tension only members
For angles with slenderness ratios measured about
their x-x and/or y-y axis
120
200
250
350
200
Construction of 132kV Overhead line between Awqad GSS &SFZ GSS
Rev. No. :A
and Associated Works (Package-1)
Volume 2 Overhead Line Specification Date : December 2010
Section 7 Supports Page :Page 8 of 38
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